The effects of corrosion, cold expansion and interference fit on the fatigue of aluminium alloy specimens containing fastener holes
One of the most vulnerable areas for the initiation and propagation of fatigue cracks in
aircraft structures is in the region of fastener holes. To reduce the incidence of fatigue
cracking a number of methods have been developed which introduce residual stresses or
induced stress fields at the fastener holes. Of these methods, two of the most widely
used in the aerospace industry involve the use of interference-fit fasteners or a
procedure for cold working the fastener holes. This investigation studies the effect of
these two technologies on the fatigue performance of specimens manufactured from
2024-T351 aluminium alloy. The effect of exposure of the specimens to corrosion
damage was also investigated.
Fatigue tests were carried out on flat plate specimens containing open plain holes and
open cold worked holes as well as on plain hole and cold worked hole specimens
containing interference fit pins. The fatigue crack growth in the specimens was
investigated under constant amplitude sinusoidal loading at a stress ratio of R=O.l and a
frequency of 10Hz. A proportion of the specimens were subjected to controlled
corrosion exposure prior to testing.Crack Growth Rate (CGR) diagrams were constructed from these experimental results
and an analysis made of crack initiation, crack propagation rate and total life.
Crack Growth Rate models were developed based on the assumption that the
dependence of CGR vs effective Stress Intensity Factor (SIF) for this material are not
affected by residual stresses in the material. Crack opening stress distributions were
derived from experimental crack growth rate data which were also confirmed by
experimental data obtained by other investigators previously.